Sex, The hierarchy of needs, Psychologist Abraham Maslow

"Psychologist Abraham Maslow in 1943 posited that humans have a hierarchy of needs, and it makes sense to fulfill the basic needs first (food, water etc.) before higher-order needs can be met."
http://en.wikipedia.org/wiki/Psychology
http://en.wikipedia.org/wiki/File:Maslow%27s_Hierarchy_of_Needs.svg

And according to this table, sex is one of the most basic needs. How come can it be one of the most basic needs? People can live without having sex with each other. Am I wrong to think like that?